when friend turns into lover

I had always been a great admirer of friendship and have treated it the most wonderful endowment by god.
While it’s the most difficult job of the world to defined what friendship is, life becomes extremely easy and enjoyable by the presence of friends.
Specially, true friends are top on the cards and they are someone you can share all the happiness and sorrows, dance for them, cry for them, help them without expecting for any acknowledgement, call them whenever you feel it like, scold them for no reason to something extremely serious, spend hours with them, yet feel like scarcity of time, trust them even after living remotely, someone who’s tears hurts, someone who’s smile relishes, so on, so on, and so on.
As I said, it’s just not possible for anyone to define what those good/true friends are.
So, it’s always great to have such friends in your life, but what if the friend is of opposite sex?
Ok, it doesn’t matter much, but while the chemistry with you and the other person is cooking nicely, many a times the friendship starts converting to a feeling of love.
There isn’t any problem to have your best/true friend as a lover, but here, the problem is not why should you love him/her, it’s about how to assure yourself whether that’s the love, and most importantly, how to express the same to the person.
While you claim that you have a nice understanding with your friend, you find it almost impossible to figure out whether the other person too feels love for you or it’s just a pure friendship.
Expressing your love to someone is itself not a easy job, but if you need to express it to a best/true friend, it’s certainly one of the hardest things.
Milians of questions bumps in mind like
Is it the love really that I’m feeling?
Does the person too love me?
Should I express it to him/her?
What if the person doesn’t feel the same and refuse?
How would I bare if the expression of love will create complications in our nice friendship?

There may be lots of such questions which hovers around, and you find yourself in bewildered state of mind.
The biggest fear is about losing the current friendship in case of refusal from his/her side, and this is what I’d like to point in here.

I just would like to ask a simple and straight forward question,
How to express your love to a very good/best/true friend, considering the scenario I’ve given above?
How to make sure that there won’t be any problem in your current friendship even if the person refuses the proposal?

Or, what do you think, shouldn’t one express his/her feeling of love to that friend?
you can write your answer in comments section, it may help a lot of folks including me!